761 FXUS64 KLUB 081745 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 1145 AM CST Fri Jan 8 2021 .AVIATION... Low CIGS and fog was quickly lifting early this afternoon at KLBB and KPVW. Conditions are expected to return to VFR in the next few hours or so. KCDS will also return to VFR later this afternoon. Additional fog and low CIG development is expected early Saturday morning to the south and west of KLBB and KPVW. Some of these lowered flight conditions may reach into the terminals but it is unclear at the moment how far down CIGS and visbys will go. && PREV DISCUSSION... /issued 321 AM CST Fri Jan 8 2021/ SHORT TERM... Low stratus clouds have begun to expand south and west out of the Texas Panhandle and southwest Oklahoma into the Rolling Plains and South Plains as of 3AM CST. Low level clouds will be stubborn to lift through the morning hours, if at all in some spots. Surface high pressure will push east through the day as upper level ridging aloft gradually flattens across the southwest US. Clouds will struggle to mix out as a robust inversion keeps winds aloft from mixing down toward the surface. There should be some partial clearing by mid afternoon especially on the Caprock. Temperatures will range from 5-10 degrees below normal both today and tomorrow. A window of clearing skies later this evening into early Saturday morning, will drop temperatures into the low 20s for most locations by early Saturday morning. But high clouds in upper level west- northwest flow aloft will be present by sunrise Saturday. Increasing southeasterly surface flow during the day tomorrow will reinforce moisture out ahead of the potent storm approaching our area in the early morning hours Sunday. LONG TERM... Confidence is increasing in the potential for widespread heavy snow across much of the forecast area Saturday night and Sunday. Models continue to be in very good agreement with the evolution of a stout upper level low progged to move from the Pacific northwest today to the 4-corners midday Saturday to southeastern New Mexico at sunrise Sunday. The NAM continues to be an outlier with its faster progression and less robust QPF while the SREF mean, the Canadian, the GFS, and the ECMWF are in remarkable agreement. Positives toward heavy snow for this event include a moist sub- cloud layer at the time of the arrival of the mid-level lift and moisture (less time spent moistening several thousand feet of air mass allowing precipitation to reach the ground), ample mid and upper level moisture, strong mid and upper level lift for about a 12 hour period, favorable temperatures in the precipitation development region for dendritic growth, and a temperature profile and surface temperatures that support an all-snow event (rather than beginning as rain or mixing with sleet, for example). This pattern matches one of four patterns identified as potential heavy snow patterns by Lambert in his 1993 TTU master's thesis and supported by more recent work by Jeff Vitale of WFO Lubbock. Lambert identified this pattern as having the greatest chance to produce heavy snowfall, the highest average snowfall, and the most widespread heavy snow of the four patterns. While matching this pattern is not a slam dunk for heavy snow, it gives a historical reference supporting the meteorological parameters listed above in favor of widespread heavy snow, defined for our forecast area as 4" or more during a 12 hour period or 6" or for 24 hours. Will ramp precip chances up further this morning and will run with the WPC forecast for snowfall which yields in excess of 4" for all but the northeastern corner of the forecast, the axis of heaviest snow extending from Friona to Lubbock to Jayton. The typical caveat applies this morning with the storm just now coming onshore to be sampled by the upper air network this morning as well as the possible shifts southward and slower with these types of systems. Given the increased confidence will issue a Winter Storm Watch for all but Hall and Childress counties for Saturday night and Sunday. The remainder of the forecast period looks to be relatively quiet with the bulk of upper level energy in the northern jet stream well to our north. Northwesterly flow aloft overhead downstream from ridging over the West Coast will temper the warming trend behind the departing storm system as will the expectation of snow cover across the forecast area. && .LUB WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Saturday evening through Sunday afternoon for TXZ021>024-027>044. && $$ 01